Provide working location/connectivity examples
Provide working location/connectivity examples

I'm getting the `invalid location` error for the provided location/connectivity examples:
```
Dulles_IE7.DSL
Frankfurt.Dial
China.custom
Dulles:Chrome.DSL
```

e.g. `https://www.webpagetest.org/runtest.php?url=https:\/\/docs.webpagetest.org&k={my_api_key}&location=Frankfurt.Dial`.

I added some examples that do work, e.g. `https://www.webpagetest.org/runtest.php?url=https:\/\/docs.webpagetest.org&k={my_api_key}&location=ec2-eu-central-1.Dial`.
WPO-Foundation/webpagetest-docs,WPO-Foundation/webpagetest-docs